2, Tang Lab, Riverside, California, United States
Solar cell efficiency could potentially be increased by exceeding the Shockley-Queisser limit through singlet fission. The Shockley-Queisser limit on photovoltaic efficiency is the theoretical maximum efficiency of a p-n junction. It states that nearly two-thirds of the light energy incident on a conventional photovoltaic material is not converted to electrical energy. Some of this lost energy could be harvested through singlet fission. Via the Dexter process, inorganic colloidal PbS nanocrystals are used to harvest the energy from triplet excitons generated by organic 1,6-diphenyl-1,3,5-hexatriene (DPH). Singlet fission (SF) is a spin-allowed process in which a high energy photon creates a singlet state in one chromophore, moiety of organic molecule responsible for absorption and emission of light. The singlet state splits into two triplet states—one in the original chromophore and one in a neighboring chromophore that is correctly orientated for electronic coupling. The Dexter process is a simultaneous, correlated transfer of an excited electron on one molecule (donor) to another molecule (acceptor) via a non-radiative pathway which depends on the wavefunction overlap between donor and acceptor. SF material has previously been made from organics, specifically polyacenes such as tetracene and pentacene. Polyacenes have been observed to have shorter triplet lifetimes and energy triplets compared to DPH. This makes DPH a prominent candidate to produce a more efficient SF material with a higher SF yield. The Wittig Reaction is utilized to synthesize DPH from derivatives with specific functional groups that allow DPH to bind to PbS. Energy transfer from DPH (donor) to PbS (acceptor) is characterized by absorbance and emission measurements.